Download - OPTICAL FIBER JOINTS & CONNECTIONS
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OPTICAL FIBER JOINTS &
CONNECTIONS
Dr. BC Choudhary, Professor
NITTTR, Sector-26, Chandigarh.
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Basic Fiber Optic Link
Transmitter Connector Cable
ReceiverCableSplice
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OPTICAL FIBER JOINTS
Technical requirement for both jointing & termination
of transmission media
Repeaters Spacing (A continuously increasing parameter)
Ranges from 40-60 km at 400 Mbits/s
100 km at 2.4 Gb/s
300 km at 1.7-10 Gb/s using SMDSFs
Number of Joints or Connections
Link length between repeaters
Continuous length of fiber
Length of fiber cable practically or conveniently installed as continuous length
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Manufacturers supply Electro-optical devices
(Sources and Detectors) with fiber optic pigtail to
facilitate direct fiber-fiber connection
IMPORTANT ASPECT IS FIBER-TO- FIBER CONNECTION
WITH LOW LOSS AND MINIMUM DISTORTION
• Source- Fiber
• Fiber- Fiber
• Fiber- Detector
FIBER JOINTS
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Two major categories of fiber joints
FIBER SPLICES: Permanent or Semi-permanent joints
Soldering
FIBER CONNECTORS: Demountable or Removable joints
Plugs or Sockets
FIBER COUPLERS: Branching devices
Splitters or Combiners
Importance in Networks
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Crucial aspect of fiber joints concerning Optical
Losses associated with the connection
1. Fresnel Reflection
Optical Loss encountered at the interfaces (Even when two fiber ends
are smooth, perpendicular to fiber axes and perfectly aligned)
A small proportion of light may be reflected back into transmitting
fiber causing attenuation at the joint.
Fresnel Reflection
• Fiber Alignment
LOSS MECHANISMS AT JOINTS
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Occurs due to step changes in refractive index atjointed interface
Glass – Air - Glass
Reflection Loss
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Fraction of light reflected at a single interface
n1 : R.I. of core, n : R.I. of interfacing medium ( = 1 for air)
2
1
1
nn
nnr
Loss in decibel due to FR at single interface
LossFres = -10 log10(1-r)
Can be reduced to a very low level using index matching fluid in the gap between jointed fibers.
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2. Deviation in Geometrical & Optical Parameters
All light from one fiber is not transmitted to another fiber ;
Because of mismatch of mechanical dimension
Three major cases :
a) Core mismatch
b) NA mismatch
c) Index Profile
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Intrinsic Losses
Minimized using fibers manufactured with
lowest tolerance i.e.(same fiber)
Losses due to:
• Fresnel Reflection
• Deviation in Geometrical & Optical parameters
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Extrinsic Losses
Losses due to some imperfection in splicing
Caused by Misalignment
Three possible types of misalignment at joint
(a) Longitudinal misalignment
(b) Lateral misalignment;
(c) Angular misalignment
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(a) Loss due to lateral and longitudinal misalignment for a 50 m core
diameter GI fiber; (b) insertion loss due to angular misalignment for joints
in two MMSI fibers with NA of 0.22 and 0.3.
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FIBER SPLICES
A permanent joint formed between two fibers
TWO BROAD CATEGORIES
• Fusion Splicing or Welding
Accomplished by applying localized heating (a flame or
an electric arc) at the interface between two butted,
prealigned fiber ends causing them to soften and fuse.
• Mechanical Splicing
Fibers are held in alignment by some mechanical means
Achieved by various methods;
o Tube Splices
o Groove Splices
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MUST HAVE SMOOTH AND SQUARE END
FACES
End preparation achieved using suitable tools - “ Cleavers”
“ Scribe and Break” or “Score and Break”
Scoring of fiber surface under tension with cutting tool
(Sapphire, Diamond or Tungsten Carbide blade)
Optical fiber end preparation: the principle of
scribe and break cutting.
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Fiber Cleavers
Handheld CleaverOne Action Cleaver
Two Action Cleaver:
Fiber cleaving &
Fusion splicing tool
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Cable Preparation Equipment
Multipack;
• Enhanced quality to prevent cracks and
fiber strength degradation.
• Allow skill-free operation of factory fiber
prep and field splicing applications.
• Equipped with a high precision tensile
strip and automatic ultrasonic cleaning
action.
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Fusion Splicing of Optical Fibers
Electric Arc Fusion splicing
• Require Fiber end surfaces
to be prepared for joint
• Heating of prepared fiber
ends to fusion point with
application of axial pressure
between two fibers.
• Positioning & alignment
using microscopes
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Prefusion Method
Prefusion method for accurate splicing
Smaller Fresnel Reflection loss
Typical Losses : 0.1 to 0.2 dB for MMF
No need for end preparation
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Fusion Splicers
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Drawback: Fiber get weakened near splice (30%)
Fiber fracture occurs near the heat-affected zone adjacent to the fused joint.
Splice be packaged to reduce tensile loading
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Protection Sleeves for spliced fibers
Protection of Joints
Fiber joint enclosures
Underground fiber splice tray
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Mechanical Splicing
Uses accurately produced rigid alignment tubes into which the
prepared fiber ends are permanently bonded.
Techniques for tube splicing of optical fibers:
(a) Snug Tube Splice
(b) Loose Tube Splice; Square Cross section Capillary
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Comparison of Two Approaches
Snug Tube Splices
• Exhibits problems with capillary tolerance requirements
• Losses up to 0.5 dB with Snug tube splice (ceramic capillaries) using MMGI and SM fibers.
Loose Tube Splices
• Avoids the critical
tolerance requirements.
• Losses 0.1 dB with loose
tube splice using MMGI
fibers.
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Ultra Splice: Reusable mechanical splice.
Average Loss 0.2 dB
Ultra Splice
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Groove Splices
V-groove splices
Insertion losses 0.1 dB using jigs for producing V-groove splice.
Use of grooves to secure the fibers to be jointed
better alignment to the prepared fiber ends.
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Elastomeric Splice: (a) Cross section (b) Assembly
Fibers of different diameters tend to be centred and hence
successfully spliced.
General loss ~ 0.25 dB for commercial product
Comprises of two elastic parts (inner with V-groove) in
compression to ensure alignment of fibers.
Elastic Tube or Elastomeric Splice
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Spring Groove Splice
Springroove Splice : (a) Expanded overview
(b) Cross-section Schematic
Mean Losses 0.05 dB with
MMGI Fibers.
Practically used in Italy.
Utilizes a bracket containing two cylindrical pins, which serve
as an alignment guide for two prepared fibers.
An elastic element (a spring) used to press the fibers into groove
and maintain alignment of fiber ends.
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Alignment of secondary elements around the bare fibers
• Increased ruggedness
• Easy ground and polish of fiber end
• Better termination
Drawbacks:
Time consuming for termination
Increased losses due to tolerances on secondary elements
Fiber misalignment.
Secondary Alignment Techniques
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Glass capillary tubes (Ferrules)
MMF mechanical splice using glass capillary tubes.
Fixing of glass ferrules
Alignment sleeve of metal or
plastic in which glass tube
fibers are aligned
Average loss 0.2 dB
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Rotary Splice
• Built-in offset and rotation, for
excellent alignment
• Alignment accuracy of 0.05 m
using three glass rod alignment
sleeve. ( necessary for SMFs; 8-10
m MFD)
• Mean Losses 0.03 dB using
Index matching gels (Not affected
by skill levels of the splicer).
Used in large installations in
USA
Rotary Splice for SMF:
(a) Alignment using glass ferrules
(b) Glass rod alignment sleeve
Use glass capillary tubes for fiber termination with small
eccentricity.
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MULTIPLE SPLICES
Splice Losses:
• Ranging 0.04 to 0.12 dB- MM GI fibers
• 0.13 to 0.4 dB – SM fibers.
Commercially available for splicing number of fibers
simultaneously
• Simultaneous Splicing of Five fibers in 5 minutes;
• 15 minutes for five single fusion splicing.
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A. Silicon Chip Array
Multiple fibers splicing using a Silicon chip array
Average Splice loss 0.12 dB.
Utilize trapezoidal grooves of a silicon chip using a comb structure
for fiber laying and top silicon chip
End faces ground & polished after curing.
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Moulded from glass filled polymer resin
Direct mass splicing of 12 fiber ribbons with simultaneous end
preparation using ribbon grinding and polishing procedures.
Fibers positioned in grooves in glass filled plastic substrate.
Vacuum technique to hold fibers at position whilst cover plate is applied.
V-groove polymer resin ribbon fiber splice.
Spring clips to hold assembly
and hole in cover plate for index
matching gel.
Average Splice Losses
0.18 dB with MM fiber.
B. V-groove flat Chip
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FIBER CONNECTORS
Demountable fiber connectors More difficult to achieve than fiber splices
Must maintain similar tolerance requirements, but in a removable fashion.
Must allow for repeated connection and disconnection without problems for
fiber alignment - without degradation in performance.
Must protect the fiber ends from damage – due to handling
Must be insensitive to environmental factors ( e.g. moisture & dust)
Must cope with tensile load on the cable and can be fitted with relative ease.
Should ideally be a low cost component,
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Fiber Termination : protects and locates the fiber ends
Fiber end Alignment : provide optimum optical coupling
Outer shell : maintains the connection and fiber alignment, protects the fiber ends from the environment and provides adequate strength at the joint.
Three Major Parts:
Losses in the range 0.2 to 0.3 dB
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A. Butt Jointed Connectors
Alignment of two prepared fiber ends in close proximity
(butted) to each other so that the fiber axes coincide.
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B. Expanded-Beam Connectors
Utilize interposed optics at the joint in order to expand the
beam from the transmitting fiber end before reducing it
again to a size compatible with the receiving fiber end.
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Cylindrical Ferrule Connector
Ferrule Connectors: (a) structure of a basic ferrule connector;
(b) structure of a watch jewel connector ferrule.
• Preparation of fiber
ends before fixing the
ferrules
• Insertion Losses 1 to 2
dB with MMSIF
• Watch jewel for close
end approach and
tolerance requirement
Glass Ferrules with central drilled hole
Concentric alignment sleeve
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Ceramic Capillary Ferrules
Outstanding
• Thermal,
• Mechanical
• Chemical Resistance
ST series multimode fiber connector using ceramic
capillary ferrules.
Ferrules made from ceramic material
End preparation after fixing ceramic ferrules
Average Losses
0.2 dB with MMGI
0.3 dB with SMF
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Commonly Used Connectors
FC Connectors ST Connectors SC Connector
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DIN Connectors
(Spring loaded free-floating
Zirconia ceramic ferrule)
MTRJ Connector
SMA Connector
Biconic Connectors D4 Connectors
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Biconical Connectors
Mean insertion losses 0.21 dB with connectors of 50m
diameter GI fibers.
Cross-section of biconical connector
Widely used as part of jumper cable
Fiber end faces polished after plug attachment
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Double Eccentric Connector
Does not rely on a concentric sleeve approach
Consists of two eccentric cylinders within outer plug.
Mean insertion loss 0.48 dB with MMGIFs reduces to
0.2 dB with index matching gel.
Also used with SMFs giving losses 0.46 dB.
An active assembly adjustable,
allowing close alignment of fiber
ends
Operation performed under
inspection microscope or peak
optical adjustment.
Connector Structure
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Duplex Fiber Connector
Developed to provide two way communications
Uses ferrules of different types
Mostly used in LANs
Commercially available
for use in FDDI loss of
0.6 dB.
Media interface plug with DFC
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Multiple Fiber Connectors
Metal guiding rods and coil
springs for precise alignment
Average Losses
• 0.8 dB with MMFs
• Reduced to 0.4 dB using
index matching fluids
(a) Fiber ribbon connector (b) SM Ten fiber
connector.
Utilizes V grooved Silicon chips for mounting
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EXPANDED BEAM CONNECTORS
Collimating and refocusing the light from one fiber into the other.
Principle of Operation
Very attractive for multi-fiber connections and edge
connections for PCBs
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Lens Coupled Expanded beam connectors
(a) Two Micro lenses connector (b) Moulded plastic lens connector
Average Loss 1 dB, reduced to 0.7 dB with AR coating
Utilize spherical micro-lenses ( 50 m ) for beam expansion
and reduction
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GRIN-rod Lenses
Arose from development of GI fiber waveguides
A cylindrical glass rod 0.5 to 2 mm in diameter with parabolic refractive
index profile.
Light propagation is determined by the lens dimension and wavelength of
the light.
Produce a collimated output beam with divergent angle of 1o to 5o from
light source.onto the opposite face of lens
An alternative lens geometry to facilitate efficient beam expansion and collimation
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GRIN-rod Lenses
• Ray propagation determined by paraxial ray equation
Solution is
r = k1cos A1/2 r + k2 sin A1/2 r : A sinusoidal path
Traversing of one sinusoidal period : one full pitch
dr
dn
ndz
rd 12
2
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Various fractional pitch GRIN-rod lenses
0.25, 0.23, 0.29 etc.
SELFOC from Nippon
Sheet Glass Co. Ltd.
Losses 1 dB
Average Losses
0.2 dB with MMGI
0.3 dB with SMF
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Fiber Reels, Connectors & Patch cords
Connectors
Adapters
Patch cords
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Fiber Splicing and Connectorization kits
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